— Data not collected; the variable was not used at the indicated grade.
NOTE: "Estimation ID" is a unique eight-character identification number assigned to identify each group-defining variable corresponding to a particular background or subject area question within the entire pool of such variables. The first four characters identify the origin of the variable: BACK (student background questionnaire), SCHL (school questionnaire), SUBJ (subject area questionnaire), TCHR (background part of teacher questionnaire), and TSUB (subject classroom part of teacher questionnaire). The second four digits represent the sequential position within each origin group. "Database ID" is a NAEP database identification number assigned to the group-defining variables commonly used in NAEP. "Teacher Questionnaire ID" labels each background question within the printed questionnaire. Variables that come from sources other than background questionnaires have no such identification. An "X" indicates that the group-defining variable was available and used in the population-structure model at the indicated grade.
SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2000 Science Assessment.